Traditional pressure sensitive labels are supplied to the user affixed to a release liner. These release liners are typically silicone coated, and, as such, are not usable as sources for recycled paper. In an effort to reduce cost, improve efficiencies, and reduce environmental impact, consumer demand for labels without liners has increased in recent years. The most common forms of these labels are “linerless labels” and “activatable labels”.
“Linerless labels” have a sticky side and a release-coated side so they can be wound upon themselves into rolls. The use of these linerless labels requires either preprinting or special printers that are configured to print on release coating. The equipment used to manipulate linerless labels includes special rollers and platens that are configured to contact the sticky side of the labels. Despite many improvements in this equipment, adhesive buildup still occurs in various sections of the equipment. Because of these shortcomings, and also the high price of the final sticky “linerless” product, these linerless labels have not received wide customer acceptance.
“Activatable labels” are supplied to the end user in a non-tacky state, and then the labels are activated, i.e., the label's adhesive is activated, to a tacky state just prior to application to the intended object. Most often, activatable labels are printed with indicia prior to activation. Known activation schemes include the use of ultraviolet (“UV”) energy to heat the adhesive (see U.S. Pat. No. 6,492,019 to Shipston et al.), corona treatment to activate the surface (see U.S. Pat. No. 6,326,450 to Shipston et al.), radiant heat to warm the adhesive (see U.S. Pat. No. 6,500,536 to Yamada et al.), moisture to activate a rewettable adhesive (see U.S. Pat. No. 6,803,100 to Hintz et al.), microencapsulating an activator material, which can then be crushed to allow the activator to mix with the rest of the formulation and activate the adhesive (see U.S. Pat. No. 7,026,047 to Krolzig), overcoating the adhesive with a detackifier layer, which is later removed by heat or mechanical means (see U.S. Pat. No. 5,569,515 to Rice et al.), and ultrasound energy to activate the adhesive (see U.S. Pat. No. 5,702,771 to Shipston et al.).
By far, the most common activation scheme utilizes heat activation, i.e., the activation of the label using heat. For heat activation, various techniques have been proposed. These include the use of the following: heated drums or rollers (see U.S. Pat. Nos. 5,749,990 and 5,480,502 to Rello et al.), direct contact with the heating element (see U.S. Pat. No. 6,388,692 to Iwata et al. and U.S. Pat. No. 6,501,495 to Ichikawa et al.), microwave energy (see U.S. Pat. No. 3,461,014 to James), heated belts in contact with the adhesive (see U.S. Pat. No. 4,468,274 to Adachi and U.S. Pat. No. 6,031,553 to Nagamoto et al.), and infrared (“IR”) and near infrared radiation (“NIR”) (see U.S. Pat. No. 3,247,041 to Henderson and U.S. Pat. No. 4,156,626 to Souder). In addition, general methods for heating using radio frequency (“RF”) energy, inductive heat, radiant heat, and visible light also are well known and could be applied to this list of activation methods. These techniques have all proven useful at low-speed operations, but as application speeds increase, these methods all suffer in that the exposure times of the labels to the heating elements must somehow be increased in order to gain sufficient heating. Either the size or the cost of the units capable of supplying sufficient heating has thwarted high-speed applications.
One way to overcome the need for larger or longer heaters is to increase the ability of the adhesive to absorb the energy from the heating devices. U.S. Pat. No. 4,156,626 to Souder and U.S. Pat. No. 6,043,190 to Ichikawa et al., and U.S. Patent Application Publication Numbers 2003/0041963 and 2004/0166309 to Gong et al. all describe the use of NIR absorbers to increase the energy absorbance by adhesives. Hence, the use of NIR absorbers and high-intensity NIR lamps might appear to be a viable route for activating the adhesive. Although satisfactory in many respects, disadvantages exist involving currently known activatable labels, labeling systems, and related methods.
Hence, there remains a need for a label without a liner and a related method of high-speed activation of the label. The present invention satisfies these needs.